The application of the hottest DELTA servo in the

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The application of DELTA servo in slow wire cutting machine tool

Abstract: This paper discusses the motion control technology of slow wire cutting machine tool, which accounts for more than 60% of the total number of EDM machine tools at home and abroad. The stable tracking error during the ultra-low speed operation of 0.5~0.2rpm and the debugging of large inertia servo system are mainly discussed

key words: wire cutting Delta Electromechanical large inertia servo

1 introduction

wirecutelectricaldischargemachining (WEDM), sometimes called wire cutting. Its basic working principle is to use the continuously moving fine metal wire (called electrode wire) as the electrode to etch the metal and cut the workpiece by pulse spark discharge. Wire cutting is mainly used to process various workpieces with complex and precise shapes, such as punch, die, punch and die, fixed plate, discharge plate, etc. of blanking die, forming tool, template, metal electrode for EDM, various micro holes, slots, arbitrary curves, etc. it has the outstanding advantages of small machining allowance, high machining precision, short production cycle, low manufacturing cost, and has been widely used in production, At present, WEDM machines at home and abroad account for more than 60% of the total number of EDM machines

2 slow wire cutting machine tools

2.1 classification of wire cutting machine tools

according to the different running speeds of electrode wires, wire EDM machine tools are usually divided into two categories: one is high-speed wire cutting machine tools (WEDM-HS), whose electrode wires do high-speed reciprocating motion. Generally, the wire walking speed is 8 ~ 10m/s. electrode wires can be reused and the processing speed is high, However, rapid wire walking is easy to cause electrode wire jitter and reverse pause, which will reduce the processing quality. It is the main machine type produced and used in our country, and it is also the original WEDM mode in our country; The other is low-speed WEDM-LS, whose electrode wire moves in a low-speed unidirectional direction. Generally, the wire speed is less than 0.2m/s, and the electrode wire is no longer used after discharge. It works smoothly, evenly, with small jitter and good processing quality, but the processing speed is low. It is the main model produced and used at home and abroad. This paper introduces the application case of delta asd-ab servo in the slow traverse machine tool. The slow wire processing machine is shown in Figure 1. The workpiece processed by the slow wire walking machine is shown in Figure 2

Figure 1 slow wire cutting machine tool

2.2 structure of wire cutting machine tool

as the main components of machining machine tool, slow wire walking and fast wire walking include:

(1) host: including bed, coordinate workbench, wire walking mechanism, etc

(2) pulse power supply: convert AC current into unidirectional pulse current of a certain frequency

(3) the control system controls the movement of the machine tool, which is the focus of this paper

(4) working fluid circulation system: provide clean and pressurized working fluid

Figure 2 workpiece processed by the slow traverse machine tool

3 motion control based on DELTA servo technology

3.1 hardware introduction

the control part is the upper computer system and servo system:

(1) upper computer: it is a special NC controller for the slow traverse machine tool based on PC architecture

(2) servo system: two sets of delta asd-ab10212ma servo controllers and delta ecma-g31309es large inertia servo motor

(3) mechanical transmission: the servo motor is directly connected to a screw rod with a pitch of 6mm

3.2 technical difficulties

the main technical difficulty of servo application on slow wire walking machine tool is to maintain a stable tracking error during the ultra-low speed operation of 0.5~0.2rpm, and the tracking error must be less than 2 pulses. In fact, such ultra-low speed technical requirements are closely related to the processing characteristics of slow wire walking machine tools. The diameter of the electrode wire of the slow wire walking machine tool is usually 0.03~0.35mm, and the total area of the center line cut on the workpiece when processing the workpiece can be up to about 350m ㎡/min. the workpiece processed by the slow wire walking machine tool is different from that of the fast wire walking machine tool, which usually requires high processing accuracy and great processing thickness. This has high requirements for the feed speed of the slow wire walking machine tool. The speed must be within a certain range. Too fast speed will cause incomplete processing, leaving rough traces of different depths on the surface of the workpiece, making the surface roughness worse, At the same time, ELG carbon fiber company (coseley will increase the vibration of electrode wire, which is easy to cause wire breakage! As for the tracking error of servo system less than 2 pulses, it is because the processing principle of wire cutting is that the continuous discharge between positive and negative electrodes burns the surface of the workpiece, that is to say, a certain distance should be maintained between the two electrodes, which can neither contact together to cause short circuit, nor too far away to cause open circuit!

4 large inertia servo system debugging

4.1 system debugging

There are many difficulties in the debugging process, because the overall load of the customer's machinery is very large, and the processing tank must be filled with water during the processing process, which makes the load inertia and load quality greater, and increases the difficulty of servo control. In order to ensure the tracking error of the two pulses, the gain of the servo controller must be maintained at a high level. However, since almost the name and specification of the sample do not allow any vibration, the gain of the servo control system cannot be too large, that is, to find a balance point between the stable response level and the stable control balance. The selection of this balance point is the key to our debugging

since the running speed of the equipment cannot exceed 200rpm required by our debugging software to estimate the load inertia, the parameters can only be set through continuous tests to find the best gain parameters, that is, the servo parameters related to gain (position control gain), (position feedforward gain), (position feedforward gain smoothing constant), (speed control gain), (speed integral compensation), As well as those related to resonance (resonance suppression low-pass filtering), (resonance suppression notchfilter) and (resonance suppression notchfilter attenuation rate) carry out continuous test settings and operation tests. The main function is to maintain the position environmental control. In recent years, the number of plastic machines imported into China is also rapidly promoting the response level, and the main function is to maintain the response level of speed loop control. These two values are the basis of servo response, The main function of sum is to reduce the position control error and speed control error. Adjusting these two values to a high position can significantly reduce the tracking error. The function is to greatly reduce the running vibration of the transmission mechanism

at the beginning of debugging, quickly adjust the servo response level to the highest control level that does not make the servo motor run with vibration. At this gain level, the operation effect of the servo motor is that the servo system runs at 0.5rpm, and the follow-up error basically remains within the range of 2 pulses, but it will jump to 3-4 pulses at some points of operation. This is not allowed for the operation of the slow wire walking equipment, and the operation effect must be improved by adjusting the servo gain, because the jump of such tracking error is due to the change of the load of the servo system at a certain operation point, and because the response of the servo system is not fast enough, the tracking error will increase. Through the above analysis, what needs to be achieved is to improve the response level of the servo system without any vibration during the operation of the servo motor. In order to not only prevent the motor from vibrating, but also improve the gain level, only by increasing and reducing the vibration of the mechanism transmission, can we improve and thus improve the overall gain level of the servo system and the response of the higher position. At the same time, we can't adjust the value of too high, because it will affect the position tracking error

when the increment adjustment is already ideal, start the trial cutting of the installed workpiece. During the trial cutting process, a very abnormal phenomenon was found, that is, when the x-axis was fed at the speed of 0.3rpm, the tracking error of the y-axis would have a continuous jump. At that time, the y-axis had no signal input at all, so there should be no movement. There are only two possibilities for such a situation: signal interference and mechanical vibration! It is judged that when the x-axis moves at a certain speed, the y-axis will have resonance! Use our debugging software Asda_ A_ SW find the resonance frequency, eliminate the resonance, and the commissioning is completed. The grabbing of resonance suppression frequency points is shown in Figure 3

Figure 3 resonance suppression frequency point

4.2 workpiece test

as a machining machine tool, we must prove whether our servo can meet the application occasions of slow wire walking machine tool through machining trial cutting. Figure 4 is the effect diagram of the workpiece processed by delta asd-ab servo. Figure 4 shows that the surface finish is tested after grinding off a part of the oxide layer. The processing effect from No. 1 to No. 3 is getting better and better. From the perspective of processing effect alone, the surface finish of No. 3 can be close to the processing effect of the 17 bit encoder high-precision servo motor of the original servo system

Figure 4 test of machining trial cutting workpiece

5 conclusion

Delta asd-ab servo is mainly used in the feed control of the control system. How the servo motion performance is directly related to the machining accuracy and surface roughness of the workpiece. The customer originally used a servo system of a well-known foreign brand, whose servo motor is a 17 bit high-line encoder, while Delta asd-ab servo system uses an ECMA motor matched with asd-b series servo system, whose encoder is only a 2500 line low line servo encoder. The machining accuracy and surface roughness of the slow traverse machine tool with delta asd-ab servo system are almost the same as those of the original 17 bit high-speed encoder servo system. Thus, the manufacturing cost of customers has been greatly compressed without reducing the performance, and the market competitiveness of their products in the slow wire processing machine tool has been improved

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